The Grain Size Evolution Mechanism of A517Q Alloy Steel Fabricated by Laser and Wire Additive Manufacturing Assisted with Different Ultrasonic Vibration Treatments

Additive manufacturing (AM) usually leads to the epitaxial growth of columnar grains in the deposition layer along the construction direction, typically resulting in the decrease in mechanical properties. In this study, A517Q alloy steel was fabricated by laser and wire additive manufacturing (LWAM) assisted with ultrasonic vibration (UV) treatment. The microstructure characteristics of A517Q alloy steel under different UV affected were investigated by OM, XRD, SEM, and EBSD. Compared with the sample without UV, the percentage of equiaxed grains in samples with dual UV increased by 90%. Due to the optimization of grain structure, the tensile strength of the sample with dual UV increased by 29% and the elongation had also been improved. The results showed that due to the cavitation and acoustic flow effects of ultrasonic, the temperature gradient (G) of the molten pool reduced and the solidification rate (R) increased, thus promoting the transformation from columnar grains to equiaxed grains. In this article, the influence mechanism of dual ultrasonic vibration (UV) on the microstructure of the laser and wire additive manufacturing (LWAM) process is investigated. Since the dynamic behavior of ultrasonic during the solidification process of molten pool is difficult to observe directly, a numerical model is established to calculate the G and R; and finally the simulation results are verified by experiments.image (c) 2023 WILEY-VCH GmbH